How to Set Up mailx on Linux to Send Emails via Gmail

Sending emails from the command line in Linux can be incredibly useful for automation, notifications, or simply managing tasks efficiently. In this guide, I’ll walk you through setting up mailx— a popular command-line mail client that allows sending emails directly from the terminal, on Linux to send emails using your Gmail account. Let’s get started!

Step 1 : Install mailtutils.

First, check if mailx is installed. Open your terminal and run:

mailx -V

If it’s not installed, install it using your package manager.

On Ubuntu/Debian:

sudo apt update
sudo apt install mailutils

On CentOS/RHEL:

sudo yum install mailx

On Fedora:

sudo dnf install mailx

Once installed, verify the installation with mailx -V.

A. When installing mailx, Select General Email Configuration Type

• You’ll see a prompt titled "General type of mail configuration".

• Use the arrow keys to highlight "Internet Site" and press "Enter."

• Why? This option configures Postfix to send emails directly to external mail servers (like Gmail’s SMTP), which is exactly what we need for relaying emails.

B. Set System Mail Name

• Next, you’ll be asked for the "System mail name".

• Enter: localhost.localdomain

•   localhost.localdomain
  

• What is this? This is the fully qualified domain name (FQDN) that Postfix uses to identify itself when sending emails. For our purposes—relaying through Gmail—it’s not critical what you choose, since Gmail will handle the actual delivery. However, localhost.localdomain is a safe, generic choice for a local or test system.

• Alternative: If your server has a real domain (e.g., myserver.example.com), you can use that instead. To check your system’s hostname, run:

•   hostname -f
  

Once you’ve entered the system mail name, the installation will complete, and postfix will be ready for further configuration.

Step 2 : Generate a Gmail App Password

Gmail requires secure authentication, so we’ll use an App Password. You can create gmail password using the following link : https://account.google.com/apppasswords

Generate and copy the 16-character App Password. Keep it safe—you’ll need it soon!
Sample Password format :

bugc musn equg wscb

Step 3 : Configure Postfix

Next, we’ll edit Postfix’s main main.cf configuration file present on path /etc/postfix/main.cf

1. Backup the Configuration: Always take a backup before making changes:

    sudo cp /etc/postfix/main.cf /etc/postfix/main.cf.bkp
   

2. Edit main.cf configuration file : Open the file in a text editor:

    sudo vim /etc/postfix/main.cf
   

3. Add or modify these lines at the end of the file:

    # Gmail SMTP relay
    relayhost = [smtp.gmail.com]:587
   
    # Enable SASL authentication
    smtp_sasl_auth_enable = yes
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
    smtp_sasl_security_options = noanonymous
   
    # Enable TLS encryption
    smtp_use_tls = yes
    smtp_tls_security_level = encrypt
    smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
   

• relayhost : Specifies Gmail’s SMTP server and port 587 (STARTTLS).

• smtp_sasl_* : Configures SASL authentication with the hashed password file.

• smtp_tls_* : Ensures encrypted communication with Gmail.

Step 4 : Configure SMTP Authentication

Postfix uses a SASL (Simple Authentication and Security Layer) password file to store Gmail credentials securely.

1. Edit the SASL Password File: Open /etc/postfix/sasl_passwd with a text editor (create it if it doesn’t exist):

    sudo vim /etc/postfix/sasl_passwd
   

   Add this line, replacing <your-email@gmail.com> and <your-app-password>:

    [smtp.gmail.com]:587    <your-email@gmail.com>:<your-generated-app-password>
   

   Example :

    [smtp.gmail.com]:587    test-example@gmail.com:bugc musn equg wscb
   

   Save and exit (:wq in vim).

2. Secure the File: Restrict permissions to protect your credentials:

    sudo chmod 600 /etc/postfix/sasl_passwd
   

3. Create a Hashed Database: Convert the password file into a format Postfix can read:

    sudo postmap /etc/postfix/sasl_passwd
   

   This generates /etc/postfix/sasl_passwd.db. Verify it exists:

    ls -l /etc/postfix/sasl_passwd.db
   

   You should see the .db file in the directory.

Step 5 : Restart Postfix

Apply the changes by restarting the Postfix service:

sudo systemctl restart postfix

Ensure it’s running:

sudo systemctl status postfix

Step 6 : Test Sending an Email

Use the mailx command to test your setup:

echo "This is a test email body" | mailx -s "Test Email via Postfix" <recipient@example.com>

Replace <recipient@example.com> with the target email address. If successful, the recipient should receive the email, and it’ll appear in your Gmail "Sent" folder.

You’ve now configured Postfix to send emails through Gmail! This setup is ideal for system alerts, cron job outputs, or scripted notifications.

Troubleshoot

If the email doesn’t send:

• Check Logs: View Postfix logs for errors:

    sudo tail -f /var/log/mail.log
  

• App Password: Ensure it’s correct (no extra spaces). You can also check Step 2 to check the password format.

• Firewall: Verify port 587 is open (sudo ufw allow 587 if using UFW).